| Because of its good mechanical properties and affordable prices,steel has became an important material in modern manufacturing industry.However,steel was very prone to corrosion in humid enviroments.The forming and processing performance of coated steel plates prepared by commonly used processes such as hot dip plating,thermal spraying,and embedded Al infiltration is poor.It is necessary to improving the corrosion resistance and formability of coated steel plates.by adopting reasonable coating preparation methods and processes.In this research,the Al/Si composite coating was prepared by magnetron sputtering with co-sputtering Al target and Si target,and the Al/Si multilayer coating was prepared by Si target sputtering,Al/Si target co-sputtering and Al target sputtering in turn.On this basis,the Al/Si coated steel plate was post-treated by subsequent heat treatment process.The corrosion resistance and formability of Al/Si composite and multi-layer coated steel plates were studied,and the corrosion protection mechanism of the coatings was analyzed.The research contents and main conclusions are as follows:(1)Al/Si composite coating with different Si content were prepared by magnetron sputtering.The results showed that the surface morphology after magnetron sputtering was more uniform and dense with the increase of Si content The particle size of the coating was about 300 nm,flat and compact after 1.5 h cosputtering deposition of Al target 160 W and Si target 80 W(Al/Si80-Q235).The 3-point bending test showed that compared with the pure Al coating(Al-Q235)deposited for 1.5 hours,it was found that the mechanical properties of Q235 coated with Al/Si coated did not change much,while the bending strength of co-sputtered and deposited for 4 hours with Al target 160 W and Si target 80 W(Al/Si80(4h)Q235)was 306.9 MPa.(2)The magnetron sputtering Al/Si composite coated was treated by heat treatment.The experimental results showed that metallurgical bonding occurs between the coated and the substrate after heat treatment,and Fe-Al-Si alloy compound was formed.The surface roughness of materials containing Si element was approximately 0.15 μm,far less than the surface roughness of Al-Q235(0.6μm).The bending strength of Al/Si80-Q235,increased by 54.0%,compared to Q235.The electrochemical test results showed that the self corrosion current densities(icorr)of Q235 and Al/Si80-Q235 were 36.104 and 1.690 μA/cm2,respectively.Due to the addition of Si element,the corrosion resistance of Al/Si composite coated steel plate was significantly improved after heat treatment,providing protection for the substrate.(3)Al/Si multilayer coated were prepared by magnetron sputtering by changing the deposition time length ratio of the first layer of pure Si coated and the third layer of pure Al coated.The Al/Si multilayer coatings were heat treated by heat treatment process.The effects of multilayer structure,temperature and pressure on morphology,structure and mechanical properties were studied.The surface of the multilayer coated was smooth and compact.The surface morphology and roughness of the magnetron sputtering multilayer coated prepared with different deposition time length ratios had not changed significantly.The thickness of the Al/Si multilayer coated was about 5.1 μm.With the increase of temperature and pressure,the surface morphology and density of the coated first deteriorate and then improve.When the heat treatment temperature was 450℃and the pressure was 10 MPa,the surface roughness of the coating also increases from 0.047±0.015μm to 0.061±0.019 μm with the deposition time ratio increases from 0.5 to 2.When the deposition time ratio is 2(Al/SiM2-Q235),the surface defects were the least,the coated structure was the densest,and the hardness of the coated also increases from 157.65 HV to 166.51 HV.(4)The formability and corrosion resistance of Al/SiM2-Q235 samples were studied using three-point bending and electrochemical corrosion testing.Through qualitative testing,it was found that the bonding force of Al/SiM2-Q235 sample under 10 MPa pressure at 450℃ was better than that of the sample without pressure at 450℃.Through the 3-point bending experiment,it was found that the bending strength under 10 MPa pressure increased by 3%compared to that without pressure.When subjected to the same displacement under pressure,the number and size of surface cracks in the former were significantly smaller than those in the latter.Through corrosion experiments,it was found that after soaking for 24 h,the surface coating structure of the sample under pressure of 10 MPa was intact,and the self corrosion current density was 1.193 μA/cm2,which was 30%lower than that of the sample without pressure.In this research,Al/Si coated with smooth surface,compact structure and good interface bonding performance was prepared on Q235 substrate by Magnetron sputtering composite heat treatment,which laid the foundation for the preparation of Al/Si coated steel plate with excellent formability and corrosion resistance. |
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